1. Field of the Invention
The present invention relates to a substrate handling apparatus for handling a substrate such as a semiconductor wafer and an ion implantation apparatus for implanting ions into the substrate.
2. Description of the Related Art
As semiconductor wafers to be processed have become larger in diameter, batch-processing ion implanters for simultaneously processing a plurality of semiconductor wafers are going to be replaced with single-substrate-processing ion implanters which process one semiconductor wafer at a time. As an example, the single-substrate-processing ion implanter has two multi-articulated robot arm assemblies (substrate holding robots or substrate holding devices) with respect to one ion beam source, for holding and sequentially exposing substrates such as semiconductor wafers to an ion beam. These articulated robot arm assemblies allow the ion implanters to operate efficiently. The articulated robot arm assembly, which can be extended and contracted, moves a substrate such as a semiconductor wafer in a direction perpendicular to the ion beam to allow the ion beam to be applied to the substrate in their entirety, and also replaces the substrate with a new substrate such as a semiconductor wafer.
The single-substrate-processing ion implanter also has two load-lock chambers for placing therein cassettes storing a plurality of substrates such as semiconductor wafers, positioned in confronting relation to the articulated robot arm assemblies, respectively. Feed robots for transferring substrates are disposed between the load-lock chambers and the articulated robot arm assemblies, thus constituting two parallel feed lines. Substrates such as semiconductor wafers are reciprocally transferred by the feed robots along the feed lines between the cassettes and the articulated robot arm assemblies (substrate holding devices).
In the above single-substrate-processing ion implantation, since the substrate holding devices and the cassettes are provided exclusively for respective groups of substrates such as semiconductor wafers, the movement of the substrates is limited, and cannot flexibly be adapted to various different operating conditions. For example, if two successive substrates are made defective by an ion implantation failure due to a malfunction of an ion source or the like, then the subsequent processing is tedious and time-consuming because the two defective substrates need to be returned to the respective cassettes. In some applications, buffer chambers are disposed alongside of a vacuum chamber for rearranging the inserted positions of substrates such as semiconductor wafers in the cassettes. Such buffer chambers make the ion implanter undesirably large in size because it has been customary to place the buffer chambers on both sides of the ion implanter.
It is desirable that each of the feed robots that are disposed between the load-lock chambers and the articulated robot arm assemblies has a clamp mechanism on its robot hand for reliably and quickly feeding a substrate such as a semiconductor wafer. One type of such a clamp mechanism comprises a vacuum suction mechanism. However, the vacuum suction mechanism cannot be used in a vacuum atmosphere, and tends to apply a large quantity of particles to a substrate as it contacts a wide area of the substrate. Another clamp mechanism for use on the robot hand has an actuator for opening and closing clamp fingers. The clamp mechanism with the actuator makes the robot hand complex in structure and heavy in weight, and hence makes the robot hand difficult to move quickly.
Further, each of the articulated robot arm assemblies (substrate holding robots) has a substrate holding mechanism which comprises a substrate holder base for holding a substrate, a clamp mechanism for mechanically retaining the substrate on the substrate holder base, a substrate attracting mechanism such as an electrostatic chuck for attracting the substrate under electrostatic forces (Coulomb forces), a substrate cooling mechanism for cooling the substrate, and a substrate attaching and removing mechanism including a clamp operating mechanism for operating the clamp mechanism. These mechanisms are mounted on the tip end of the articulated robot arm assembly. Inasmuch as these mechanisms are constructed of many parts that are mounted on the tip end of the articulated robot arm assembly, the articulated robot arm assembly is necessarily large in size and heavy in weight. As a consequence, the substrate holding robots have their main bodies, arm assemblies, and actuators thereof that are relatively large in size, and hence the processing chamber (ion implantation chamber) is also relatively large in size. The tendency toward larger-size substrate holding robots manifests itself as substrates such as semiconductor wafers to be handled have larger diameters.
The substrate holding robot holds a substrate such as a semiconductor wafer by mechanically pressing the outer circumferential edge of the substrate with the clamp mechanism. However, because the clamp mechanism cannot apply sufficiently strong forces to press the semiconductor wafer, it cannot bring the entire surface of the substrate into intimate contact with a thermally conductive medium such as rubber. Therefore, the substrate pressed by the clamp mechanism cannot sufficiently be cooled by the substrate cooling mechanism. This problem is serious with the single-substrate-processing ion implanters because the ion beam applied intensively to substrates one by one develops intensive heat on the respective substrates.
Each of the articulated robot arm assemblies comprises a plurality of arms coupled by joints and an arm actuating mechanism connected to a proximal end of the arms. The arms house therein a power transmitting mechanism which comprises shafts, pulleys and belts. The arms that are positioned in the vacuum chamber have their internal space open into the vacuum chamber, so that the internal space of the arms can be evacuated by an evacuating mechanism connected to the vacuum chamber. The joints by which the arms are coupled use magnetic fluid seals, and the arms are of a closed structure except for air ports with filters which are disposed on backsides of the arms. This structure serves to prevent particles produced by sliding surfaces of the arms from being scattered in the vacuum chamber.
The articulated robot arm assemblies are complex in structure construction because of the joints using the magnetic fluid seals and the filters provided on the arms, and hence cannot be serviced simply for maintenance. Furthermore, the closed structure of the articulated robot arm assemblies is not effective enough to prevent particles from being scattered in the vacuum chamber. In addition, particles that can be trapped by the filters are subject to a certain limitation on their diameters.